Have you checked the white/light blue wire for a short to ground?
A problem like this can be very frustrating.
It's time to rationalize the problem.
Something is making the idle run high. In order for this to take place it has to be getting air.
Where is this air coming from?Brake
A hidden vacuum leak?
Or is it the idle air control?
If you monitor the ground circuit at the idle air control to see if it is grounding out that will verify the air source.
Once verified you can continue to look there.
If it isn't then you need to look elsewhere.
You could also run with the IAC disconnected. You would have to use the throttle to keep it running.
Have you ever had it hooked up to a scanner capable of reading the data stream from the other sensors?
Perhaps there is one that is sending a wrong signal (such as a tach/RPM reading) and the PCM sends a IAC open command.